The invention relates to a coextrusion film that has a layer of thermoplastic elastomer. Such a coextrusion film is provided for the production of composite elements, where in particular lamination with a stretchable but typically inelastic nonwoven material is intended. Such a laminated composite web can, for example, be provided as elastic tape or as elastic band of disposable hygienic products such as, for example, baby diapers or comparable incontinence articles. The elasticity of the laminated composite is thus achieved by a layer of thermoplastic elastomer.
In the production of a monocomponent film consisting of thermoplastic elastomer there exists the problem that traction applied to the film during handling must be kept low to ensure that intense stretching or tearing is avoided. Thermoplastic elastomers further have significant inherent adhesiveness and can quickly bond together after being rolled up on a roll, so that storage of monocomponent film consisting of thermoplastic elastomer is not possible in roll form.
A coextrusion film is known from U.S. Pat. No. 7,449,240 that has a core layer of a thermoplastic elastomer and at least one skin layer. When the coextrusion film is rolled up, the skin layer acts as a separator and thus prevents the stick core layers of adjacent turns from coming into direct contact with each other, so that bonding-together can be avoided. Although the known coextrusion film has proven itself in practice, there exists the disadvantage that first an embrittlement of the skin layer and subsequently in an additional method step of activation of the coextrusion film due to an overexpansion is required, in which the at least one stiff outer layer tears open in strips in the direction of expansion. Perpendicular to this direction of expansion, the coextrusion film remains stiff.
Laminating a monocomponent film of a sticky thermoplastic elastomer with a thin nonblocking layer of nonwoven immediately after extrusion is known from U.S. Pat. No. 7,470,340. On the one hand this process protects the elastic monocomponent film from excessive expansion during handling, and on the other hand prevents bonding together when rolled up. As immediately after extrusion of the monocomponent film, a nonwoven material must be fed in and laminated, the method is laborious. Further, the applications of the formed laminated composite are limited as a preliminary product due to the outer layer of nonwoven provided on the at least one side.
In order to avoid bonding together of sticky monocomponent films made of thermoplastic elastomers, it is further known to cover them with a powder after extrusion. According to US 2006/0225835, a powder made of polymeric material is used that melts during lamination of the elastic monocomponent film with a covering material by a hot-melt adhesive, as a result of which the stability of the composite that is to be achieved is not significantly impaired by the powder. The described method requires that the elastic monocomponent film be combined with a covering material by hot-melt adhesive, the bonding temperature of the hot-melt adhesive on the one hand, and the melting temperature of the powder on the other hand, forcibly being coordinated with each other. Further, although the powder prevents bonding together of the monocomponent films consisting of thermoplastic monomer during storage in rolls, when handling the monocomponent film, the tensions must be kept low in order to avoid uncontrolled stretching or tearing.